ECG diagnosis and classification of acute coronary syndromes

Abstract

In acute coronary syndromes, the electrocardiogram (ECG) provides important information about the presence, extent, and severity of myocardial ischemia. At times, the changes are typical and clear. In other instances, changes are subtle and might be recognized only when ECG recording is repeated after changes in the severity of symptoms. ECG interpretation is an essential part of the initial evaluation of patients with symptoms suspected to be related to myocardial ischemia, along with focused history and physical examination. Patients with ST-segment elevation on their electrocardiogram and symptoms compatible with acute myocardial ischemia/infarction should be referred for emergent reperfusion therapy. However, it should be emphasized that a large number of patients may have ST-elevation without having acute ST-elevation acute coronary syndrome, while acute ongoing transmural ischemia due to an abrupt occlusion of an epicardial coronary artery may occur in patients with ST-elevation less than the thresholds defined by the guidelines. Up-sloping ST-segment depression with positive T waves is increasingly recognized as a sign of regional subendocardial ischemia associated with severe obstruction of the left anterior descending coronary artery. Widespread ST-segment depression, often associated with inverted T waves and ST-segment elevation in lead aVR during episodes of chest pain, may represent diffuse subendocardial ischemia caused by severe coronary artery disease. In case of hemodynamic compromise, urgent coronary angiography has been increasingly recommended for these patients.

Keywords: ST-segment depression; ST-segment elevation; acute coronary syndrome; electrocardiogram; myocardial infarction; risk stratification; triage.

Figure 1

Inferior and lateral STE‐ACS. There is ST elevation in the leads II, III, aVF, and V₄–V₆. Leads I and aVL show reciprocal ST depression. ST elevation in leads V₁–V₂ represents lateral “mirror‐image” ST deviation. There is Sclarovsky–Birnbaum grade III of ischemia in leads III, aVF, and V₆.

Figure 2

The early repolarization pattern with J‐point and ST‐segment elevations in the leads I, aVL, and V₄–V₆.

Figure 3

Acute pericarditis with ST elevation in the leads I, II, III, aVF, V₃–V₆ with ST depression in aVR and V₁. PR‐segment depression in the leads aVF and V₄–V₆ and PR‐segment elevation in lead aVR is also typical of pericarditis.

Figure 4

The ECG shows ST elevation in the inferior and precordial leads, most prominently in the leads V₁–V₄. Deep S waves in the leads V₁–V₄ and a high R waves in I and aVL indicate left ventricular hypertrophy.

Figure 5

Inferior STE‐ACS. There is ST elevation in the leads II, III, and aVF and reciprocal ST depression in the lead aVL. ST depression in the leads V₁–V₄ indicates involvement of the lateral segment of the left ventricle.

Figure 6

Up‐sloping ST depressions in the leads V₃–V₅ with prominent, positive T waves. The patient had an occluded left circumflex coronary artery.

Figure 7

The “Wellens’ sign”: inverted T waves in the precordial leads, maximally in V₃–V₄. Also leads I, II, and aVF show T‐wave inversions.

Figure 8

Circumferential subendocardial ischemia: widespread (≥6 leads) ST depressions with inverted T waves maximally in leads V₄–V₅ and ST elevation in the lead aVR.

Figure 9

ST elevations in the leads V₁–V₂ and aVR with widespread ST depressions. ECG signs of left ventricular hypertrophy: deep S waves in the right and high R waves in the left precordial leads and in leads I, II, III, and aVF.